Steam generator

ABSTRACT

This invention relates to a steam generator for evaporating from a vaporizing portion (17) thereof a liquid (12) sucked up by means of a liquid sucking-up member (10) to provide a steam generator which is capable of vaporizing a liquid efficiently in a short time by application of heat from a heating unit (13) and air fed from a fan (15).

TECHNICAL FIELD

This invention relates generally to steam generators for use inhumidifiers, steam inhalers or the like which are capable of efficientlygenerating steam within a short time interval.

BACKGROUND ART

In recent years, there have been developed a number of steam generatorssuch as humidifiers, steam irons, steam inhalers, all of which havebecome popular in the market.

In particular, humidifiers and inhalers have been favorably noticed.Inhalers are effective as a measure for bronchitic or asthmaticpatients, so that many related articles have been recently developed.However, most known inhalers are arranged such that 300-400 ml of waterin a container is heated by means of an electric heater to generatesteam and a saline solution or an adrenaline solution is sprayedentrained with the steam by application of a spraying principle usingthe pressure of the generated steam. For generators of this type, ittakes approximately 7 minutes during the summer season and 10-15 minutesin the winter before steam is generated after introduction of water.Thus, most of the generators, in addition to requiring a relatively longtime duration before steam generation, also involve difficulty incontrolling the temperature of steam and no steam generation occursunless a certain level of water is provided in spite of their use for ashort time, and are poor in economy from a viewpoint of energy saving.

The humidifier is also becoming an important electric article in view ofthe growing demand for air conditioning coolers and the FF-type heatingapparatus as a preventive measure against dryness of the air when usingair conditioning coolers in the summer season or as a measure ofhumidification required when the FF type heaters are used in the winterseason.

In principle, humidifiers are divided into two groups, ultrasonic andheating types. The heating type humidifier is scarcely employed since itrequires a long time before steam is generated (as is the case withinhalers), resulting in poor economy from the standpoint of energycosts. On the other hand, the ultrasonic system is employed and since itgenerates water droplets (not steam) having a size of 5-30 μm, itappears visually that steam generated simultaneously with the electricsource being turned on; howwever, it actually takes a long time beforethe water droplets are vaporized into steam. In addition, fine waterdroplets (5-30 μm) generated from the ultrasonic humidifier does notreach the lung by adsorption with organs, and thus the ultrasonichumidifier is not so favored from a standpoint of health. As a matter ofcourse, there has been heretofore made an effort to improve ultrasonicgenerator elements in order to make finer the water droplets of theultrasonic humidifier. To obtain finer water particles requires greateramounts of electric energy or involves greater levels of noise. As aconsequence, the humidifiers which have been practically utilized from aview point of their commercial value are, in most cases, those in whichthe size of water droplets is in the range of 5-30 μm, but such size wasnot satisfactory. That is, it is medically accepted that when takinginto account an influence on human body, a particle size of below 1 μmor a steam-like particle size is most ideal.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention contemplates to efficiently generatea necessary amount of steam within a short time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front, sectional view of a steam generator showing oneembodiment of the invention;

FIG. 2 is a front view of a portion of a liquid sucking-up member ofFIG. 1;

FIG. 3 is a side view of the liquid sucking-up member;

FIG. 4 is an enlarged front view of an essential part of the liquidsucking-up member;

FIG. 5 is a characteristic graph;

FIG. 6 is an enlarged view of the liquid sucking-up member of FIG. 1;

FIG. 7 is a front view of another embodiment of the liquid sucking-upmember;

FIG. 8 is a front view of a further embodiment of the liquid sucking-upmember;

FIG. 9 is still a further embodiment of the liquid sucking-up member;

FIG. 10 is a flow chart showing a procedure of making a bactericide;

FIG. 11 is a flow chart showing another procedure of making abactericide;

FIG. 12 is an enlarged view of a heating unit;

FIG. 13 is an enlarged view of a heating unit;

FIG. 14 is an enlarged view of a heating unit;

FIG. 15 is an enlarged view of an essential part of FIG. 14;

and

FIG. 16 is a flow chart showing a procedure of making a heating unit.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIGS. 1-4, a container 1 for generating steam is divided through apartition plate 2 into a vaporizing chamber 3 and a liquid storingchamber 4. Vaporizing chamber 3 is, if required, provided with a gascharge port through which a gas is charged and a discharge port 6through which a vaporized steam is discharged. Liquid from a liquidcharge pipe 7 is maintained at a certain level by a liquid leveller 8and then introduced into liquid storing chamber 4 through a liquidcharge pipe 9.

A liquid sucking-up member 10 having capillary action extend into liquidstoring chamber 4 and vaporizing chamber 3 through a through-hole 11provided in partition plate 2.

Liquid sucking-up member 10 is immersed at the lower end thereof in aliquid 12 kept in the liquid storing chamber 4, and at its upper end itextends into the vaporizing chamber 3 and is provided with a heatingunit 13. Heating unit 13 generates heat by application of an electriccurrent from terminals 14 where required.

Vaporizing chamber 3 is arranged to be fed with a gas, such as air, whenrequired, by means of a fan 15 causing gas to flow through a gasintroduction pipe 16 and gas charge port 5.

The operation of the steam generating unit shown in FIG. 1 is nowdescribed by way of example of water vapor generation. Water is fed froma water service pipe or through an electromagnetic valve (for waterservice) into liquid charge pipe 7 and then stored through the liquidleveller 8 and charge pipe 9 in liquid storing chamber 4 as a liquid 12.This water is then sucked up by means of liquid sucking-up member 10 viaits capillary action so that it reaches a vaporizing portion 17 of theliquid sucking-up member. Portion 17 is provided to cover the outersurface of heating unit 13 disposed within vaporizing chamber 3.

The flow rate of air to be fed will accelerate evaporation from member10, i.e. an increase in flow rate of air results in an increase in anamount of generated steam. The experiment made by the present inventorsrevealed that the accelerating effect was shown when the flow rate of agas such as air which passed while being contacted with the liquidsucking-up member 10 on the surface thereof was about 0.1 m/s. It willbe noted that the flow rate of 0.1 m/s is determined under. conditionsof 1 atm., R.H. of 45% and room temperature of 20° C.

As described above, the amount of evaporating steam increases when theflow rate of gas is above 0.1 m/s but optimum conditions are obtainedwhen the flow rate is in the range of 2-3 m/s. It has been found thatwhen the flow rate exceeds 3 m/s, the amount of evaporation does notincrease proportionally to the supplied energy involved in the gas.

A relationship between the amount of evaporating water and the suppliedelectric energy was determined in cases where air was fed into container1 from charge port 5 and where no gas was charged.

FIG. 5 shows the results of the experiment.

The apparatus used for the experiment was the steam generator of theembodiment according to the invention shown in FIG. 1. The experimentalconditions are as follows: (A) No air was fed by means of the fan 15;(B) The fan 15 was controlled so that a flow rate of air which flowed incontact with the surface of the liquid sucking-up member 10 was 0.1 m/s;and (C) A flow rate of air was controlled to be 2.5 m/s by a proceduresimilar to the case of (B).

As is clearly seen from FIG. 5, even though electric power supplied toheating unit 13 is held at the save level, a greater amount ofevaporated steam is obtained in the case (B) where air is fed by meansof the fan 15 than in the case (A) where no air is fed from the fan 15and a greater flow rate of air as in (C) results in a much greateramount of evaporated steam.

A feature of the steam generating unit having such an arrangement asshown in FIGS. 1-4 resides in that since it is sufficient to vaporizewater alone which has been fed to the vaporizing portion 17 providedaround the heating unit 13, a required amount of steam can be fed over arequired period of time only 3-5 seconds after application of anelectric current to the heating unit 13. Accordingly, it is possible toalmost instantaneously generate steam without raising the temperature ofthe entire amount of water in the container to 100° C. as will beexperienced in prior art counterparts. The essential parts of the steamgenerating unit of the invention will be described in detail.

<KIND OF LIQUID 12>

As liquid 12, there can be used most of various liquids such as water,aqueous solutions, solvents, drugs, kerosene and the like.

<CONSTITUTING MATERIALS FOR CONTAINER 1>

Container 1 can be made of metals, resins, ceramics and the like. Inparticular, the inner surface of vaporizing chamber 3 and inner surfaceportion of the partition plate 2 at the side facing vaporizing chamber 3is preferably either constituted of heat-resistant, heat-insulating orflame-retarding materials or lined. For instance, it is preferable thatthe container 1 is constituted of a metal and then lined with aflame-retarding resin or enameled.

<LIQUID SUCKING-UP MEMBER 10>

Liquid sucking-up member 10 having a capillary action is desired to havea water suction rate of above 10 mm/sec. This was confirmed by a test inwhich a fiber constituting the liquid sucking-up member 10 (e.g. a glassfiber) or asbestos fiber was immersed in water colored with a colorantdye, and a height of the water sucked up in 10 seconds was measured.

Most fibrous materials show a rate of above 10 mm/sec., but among foamedmaterials there are a number of materials whose rate is below 10 mm/10sec.

A rate greater than 10 mm/10 sec. will make it possible to efficientlygenerate steam in a required amount. With rates below 10 mm/sec., theheat energy from heating unit 13 may not be satisfactorily utilized,thereby lowering heat efficiency.

The most preferable materials for the liquid sucking-up member includeglass fibers, alkali-proof fibers, silica fibers, alumina fibers and thelike. The (plain-like thick gause), Calico weave, twill weave and thelike of these fibers are most suitable for the purpose of the invention.Other materials including cloth and fabric materials made offlame-retarding fibers such as carbon fibers, asbestos and novolacfibers, metallic fibers and ceramic fibers also satisfy the purpose ofthe invention but they are slightly inferior in fiber strength,processability, heat resistance and cost to glass fibers. In addition,heat-resistant porous materials and foamed materials are usable but areinferior in processability and sucking-up ability to glass fibers.

Liquid sucking-up member 10 according to the present invention ischaracterized not only by its high capability of sucking up water usingcapillary action as described hereinabove, but also by its ability toprovide a sterilizing action for preventing propagation of bacteria.

FIG. 6 shows a liquid sucking-up member 10 having deposited on thesurface thereof a bactericide 18 such as, for example, a sparinglysoluble silver salt.

FIGS. 7-9 show the liquid sucking-up member 10 which has imparted on thesurface thereof other arrangements to provide a sterilizing function.FIG. 7 shows a liquid sucking-up member 10 which is disposed with asterilizing member 19 in the form of a plate or rod made of asterilizing metal or metal salt such as Cu, Ag, AgCl or the like.Sterilizing member 19 may be formed by depositing a sterilizing metal ormetal salt such as, for example, Cu, Ag, AgCl or the like on the surfaceof a protecting substrate. FIG. 8 shows an arrangement in which abactericide 18 composed of a sterilizing metal or metal salt is directlydeposited on part of the liquid sucking-up member 10. FIG. 9 is similarto FIG. 8 and shows an arrangement in which the liquid sucking-up member10 is constituted of a porous ceramic which has directly deposited at alower portion thereof a bactericide 18 made of a sterilizing metal ormetal salt.

Most preferable protecting substrates of the sterilizing member 19 arethose made of carbon fibers, chemical fibers, glass fibers and the like.Especially suitable chemical fibers are those which are water proof,such as vinylon, nylon and the like. These fibers are shaped in the formof threads, clothes, and non-woven fabrics and applied as the protectingsubstrate for sterilizing member 19.

FIG. 10 and 11 show procedures for making the sterilizing member 19.

That is, FIG. 10 shows a process of making, as the sterilizing member19, a plate-like band obtained by rolling AgCl and FIG. 11 shows aprocess of making the sterilizing member 19 by depositing AgCl on thesurface of a protecting substrate made of a vinylon non-woven fabric.First, the process shown in FIG. 10 is described in detail. To a AgNO₃solution was added a NaCl solution to deposit AgCl precipitate accordingto the following reaction formula

    AgNO.sub.3 +NaCl→AgCl↓+NaNO.sub.3

The AgCl precipitate is filtered and washed to remove NaNO₃ and NaCl(remaining in excess). Thereafter, the AgCl is dried, melted attemperatures of 480° to 520° C. (melting point 455° C.), and cast in theform of a plate, rod or the like. After cooling, the casting is hotrolled to obtain a sterilizing member 19 in the form of a thin film. Theprocess of FIG. 11 is now described. AgNO₃ is uniformly deposited on aprotecting substrate such as a vinylon non-woven fabric in a vessel forAgNO₃ solution and dried to remove moisture. Then, the AgNO₃ ishalogenated in a vessel of NaCl solution, washed with water and dried togive a sterilizing member 19.

The sterilizing function is now described. A useful bacteriologicalinspection for water is expressed in terms of a total number of bacteriain 1 milli-liter of water and completely sterilized water is extremelylow in number of bacteria, e.g. the standard for drinking water has beenlegally decided as below 100 bacteria per milli-liter of water. Thesebacteria are generically called general bacteria and aside from thesebacteria, colitis germs are needed to examine. It is more important tonote that there are also present in water molds to be aquatic plants(duckweeds) resembling bacteria.

It can not be said that all of these microorganisms in water are harmfulto human body but it is a matter of fact that sterilized water is betterthan propagated water.

The sterilizing effect of heavy metal ions in water is calledOligodynamic action, meaning a sterilizing effect on microorganismsshown by a small amount of a certain type of metal ions. Stated morespecifically mercury, silver, copper and like metals show a strongsterilizing action in their ionic states (Hg⁺⁺, Ag⁺, Cu⁺⁺). The metallicions serve to kill microorganisms only in an extremely small amount(10⁻⁶ M). This action may be called an oligodynamic action.

As the bactericide 18 there may be mentiond metals such as mercury,copper, silver, zinc, lead, iron and the like as mentioned above andtheir oxides, carbonates, halides, nitrates and the like, of whichmaterials showing a less ill effect are copper, silver, zinc and iron.In particular, copper, silver and their salts are excellent in economy,production process and processability, and also in sterilizing effect.Alternatively, those which are high in safety and show an excellentsterilizing effect even when used in very small amounts include silveror its salts, which show a small solubility in water and are usable overa long time and sufficient to apply in small amounts. The solubilitiesof silver and silver salts are, for example, as follows: 10⁻⁵ mol/l forsilver chloride, 10⁻⁶ mol/l for silver bromide, and 10⁻⁸ mol/l forsilver iodide, of which silver chloride is more advantageous in view ofsterilizing effect, processability, production process and cost.

<HEATING UNIT 13>

Any heating units which can supply an energy necessary for vaporizing aliquid sucked by the liquid sucking-up member 10 are suitable for thepurpose of the invention.

As a heating material, for instance, commercially available heatingwires and heating bands made of Ni-Cr, Fe-Cr, Fe-Cr-Al, Fe-Cr-Al-Y, andstainless steel are all usable. Aside from these, heating materials suchas PCT heating elements, sheathed heaters, heat pipes, heat conductors,composite heating elements which are obtained by spray coating ofelectric heating wires with ceramics on the surface thereof such as by aplasma spray coater are usable as the heating unit of the invention. Thesurface structure of heating unit 13 is now described. The heating unitis mainly made of a usual heating wire and a sheathed heater because ofeconomy and ease in attachment. When the surface is flame spray coatedwith a metal oxide (or double oxide) 20 by a spray coating means such asa plasma spray coater to shown in FIG. 12, this serves as acceleratevaporization to allow a liquid to be efficiently vaporized. That is, thecoating plays an important role in improving the efficiency of contactwith the liquid sucking-up member 10, accelerating the introduction of aliquid to the surface of the heating unit 13, serving to acceleratevaporization on the surface of the heating unit 13 as boiling stone,keeping nichrome wires insulated and the like, making it possible topermit the vaporization to proceed efficiently.

FIG. 12 shows a first coating layer made of a metal oxide (or metallicdouble oxide) 20 on the surface of the heating unit 13 made of a heatingwire or a resistor. Since the surface temperature of the heating unit 13used in the present invention is preferred to be in the range of200°-250° C., its thermal expansion does not prevent metal oxide (ormetallic double oxide) 20 such as Al₂ O₃, TiO₂ or MgAl₂ O₃ from beingdirectly coated on heating unit 13 by a plasma spraying technique.

FIG. 13 shows an arrangement in which a heat-resistant alloy 21 iscoated on the surface of heating unit 13 as a first coating layer andthen a metal oxide (or metallic double oxide) 22 as a second coatinglayer is formed thereon. This is because the difference in thermalexpansion between the heating unit 13 and the metal oxide (or metalicdouble oxide) 22 is great, the heat-resistant alloy 21 such as Ni-Cr,Ni-Cr-Al or stainless steel is formed as an intermediate coating layerso that the unit can satisfactorily withstand long periods of use withinthe heat cycle.

FIGS. 14 and 15 show an arrangement in which the porous layer of themetal oxide (or metallic double oxide) 22 is treated with a filler 23.

The process of making the heating units of FIGS. 14 and 15 isillustrated with reference to FIG. 16.

<HEATING UNIT 13>

The heating unit 13 is most preferably made of windings of a nichromewire, iron-chromium wire, Kanthanl alloy wire, Esit (Trade mark) wire,stainless steel wire and the like but other heat sources such as asheathed heater, PTC ceramister and the like may be used. The presentinvention is described with reference to a case where usual electricheating wires such as a nichrome wire are applied to heating unit 13.

<SURFACE ROUGHENING TREATMENT>

First, surface of the heating unit 13 is defatted and washed, and thenroughened by means of a general abrasive such as Al₂ O₃, SiC or the likewith a grain size of 20-100 mesh under a blast pressure of 3-5 Kg/cm².It is preferable that heating unit 13 is treated to have an averagesurface roughness (Ra) of 1-10μ when measured by the Tallisurf surfaceroughness tester. Ra values less than 1μ result in a poor coatingefficiency of the metal oxide (or metallic double oxide) 20 and Ravalues larger than 10 μ lead to a difficulty in uniform coating of themetal oxide (or metallic double oxide) 20.

<WASHING DRYING>

Since the heating unit 13 has been deposited with an abrasive orabrasion dust on the surface thereof during the course of the surfaceroughening step, it is washed with water and then well dried at 100-150C.

<FORMATION OF FIRST COATING LAYER>

The heating unit 13 used in the present invention is characterized inthat a usual heating wire is finely wound in the form of a coil to forma small-size unit of high capacity, thereby making the rise-up time(pre-purge) fast. Accordingly, due consideration must be given withrespect to electric insulation of the coil. In order to ensure goodthermal transmission to water, the surface area of the heating unit 13should be large. The above requirement can be satisfied by covering thesurface with the metal oxide (or metallic double oxide) 20 and thus theintended purpose can be attained.

Examples of material suitable for this purpose include metal oxides 20such as Al₂ O₃, SiO₂, Fe₂ O₃, Y₂ O₃, TiO₂, CaO, B₂ O₃, Li₂ O, Cr₂ O₃,ZrO₂, MgO, BeO, NiO, ThO₂, HfO₂, La₂ O₃, and CeO₃ (or spinel type doubleoxides such as MgAl₂ O₄, MnAl₂ O₄, FeAl₂ O₄, CoAl₂ O₄, ZnAl₂ O₄, MgCr₂O₄ and the like) and at least one of these compounds is preferably used.Of these, most effective and economical ones are Al₂ O₃, TiO₂, ZrO₂,SiO₂, and MgAl₂ O₄.

Methods of coating these materials include arc spray coating, flamespray coating, plasma spray coating, explosion spray coating and thelike, of which the plasma spray coating is suitable for the purpose ofthe invention. In the present invention, the first coating layer wasformed by spray coating a metal oxide (or metallic double oxide 20) byusing a Model SG-100 plasma spray coating machine of the 80 K.W. typemade by Plasma Dyne Co., Ltd., and under conditions of argon gas as anarc gas, helium as an auxiliary gas, an electric current of 1000 A and avoltage of 41 V.

The thickness of the first coating layer was found to be effective atabout (10-100)μ.

FORMATION OF FIRST COATING LAYER=FORMATION OF INTERMEDIATE COATING LAYER

A method of forming a coating of a heat-resistant alloy 21 of FIG. 6 isdescribed.

As described hereinbefore, the intermediate coating layer is disposedbetween heating unit 13 and metal oxide (or metallic double oxide) 22and should stand stably usable over a long time in the heat cycle ofheating unit 13. Most suitable materials as the heat-resistant alloy 21include Ni-Cr, Ni-Cr-Al, Fe-Cr, Fe-Cr-Al, and Fe-Cr-Ni-Al. It will benoted that the thickness layer of heat-resistant alloy 21 as anintermediate layer was found to be effective at about 5-30μ.

When the intermediate layer of heat-resistant alloy 21 (such Ni-Cr-Al)to be an intermediate coating layer is formed by spray coating on thesurface of heating unit 13 (as described above) and then metal oxide 22,such as TiO₂, Al₂ O₃, SiO₂, ZrO₂ or the like, is formed by spray coatingas the first layer, 5-30% of pores are substantially formed in thecoating layers, with the result that when immersed in water, the heatingunit 13 undergoes oxidation on the surface thereof, showing a variedresistance during long use. This entails a variation of a pre-setelectric power or disconnection in the worst case. To avoid this, asealant 23 is used. As a result of extensive study for a suitablesealant 23, it was found that both inorganic sealants such as waterglass, silica oil, alumina sol, glass powder and the like and organicpolymeric sealant such as silicone resin, fluorine resin, heat-resistantpaints and the like were effective. Of these organic polymers werepreferable and, particularly, a sealant mainly composed of fluorineresins were most effective from standpoint of moisture proof, heatstability, electric insulating property, and corrosion resistivity. Thefluorine resin is at least one resin selected from the group consistingof ethylene tetrafluoride resin, propylene tetrafluoride copolymerresin, and ethylene trifluoride resin.

<METHOD OF COUPLING THE HEATING UNIT 13 AND LIQUID SUCKING-UP MATERIAL10>

In FIGS. 2-4, there is shown a manner of coupling the heating unit 13and liquid sucking-up member 10. For instance, a plain weave liquidsucking-up member 10 made of a material having a capillary action suchas, for example, a glass fiber bundled thread is applied to cover thesurface of the heating unit 13 and a seam 24 is sewed in so that thematerial is allowed to intimately contact heating unit 13. It wasconfirmed that when water was fully impregnated in the liquid sucking-upmember 10 prior to the sewing-in of seam 23, the liquid sucking-upmember 10 was stretched to ensure good contact with the heating unit 13.

Examples are now particularly described.

<EXAMPLE 1>

A Ni-Cr wire of 0.4 mmφ was wound in the form of a coil to have an innerdiameter of 5 mmφ, a length of about 4 cm and an entire resistance of1Ω, thereby forming a heating unit 13. The heating unit 13 was thenblasted on the surface thereof and spray coated with powdery aluminahaving a particle size of 30-100 μm by a plasma spray coating to providea 20-30 μm thick alumina layer in a manner as shown by the metal oxide21 of FIG. 12. Then, as shown in FIG. 2, heating unit 13 was coveredwith a liquid sucking-up member made of a thick fabric of glass fiberbundled threads to have a width of 4.5 cm and a height of 8 cm as shownin FIG. 2, and was disposed as shown in FIG. 1.

In this arrangement, the fan of FIG. 1 was stopped and evaporated steamalone was generated. Terminals of a slide auto-transformer wereconnected to electric terminals 14, through which an electric currentwas applied at an electric power of 80 W. 5-8 seconds after application,steam was vigorously discharged from the discharge port 6.

To apply the above arrangement as a humidifier, air was fed so that aflow rate of air from the fan 15 was controlled to have 40 cm/sec at thedischarge port 6 and the heating unit 13 was applied with an electricpower of 30 W. As a result, 3-4 seconds after the application, steam wasgenerated from discharge port 6.

As described above in detail, the steam generating apparatus of thisexample is compact and lightweight and can generate steam efficiently onapplication of only a small electric power.

It will be noted that it is very important to constitute the innersurface of the vaporizing chamber 3 with a heat-insulating material.That is, steam generated at the heating unit 13 and the vaporizingportion 17 is again condensed on the inner surface layer of thevaporizing chamber 3. This is why it is important to constitute theinner surface of the vaporizing chamber 3 with an insulating material ofsmall heat capacity.

<EXAMPLE 2>

There were, respectively, used the liquid sucking-up member 10 (glassfiber) used in Example 1 which were subsequently deposited directly withbactericides on the surface thereof (No. 2 and No. 3 of Table 1 shownbelow), the liquid sucking-up member 10 which were subsequently providedwith a plate-like band of a vinylon non-woven cloth deposited with abactericide on the surface thereof (No. 4 of Table 1 shown below), andthe liquid sucking-up member 10 which were subsequently deposited withbactericides (metal plate, metal salt plate) (No. 5, No. 6 of Table 1)to determine the number of propagating bacteria in relation to days ofstorage of water in the liquid storing chamber 4 of the steam generatingunit, i.e. a bactericidal activity, with the results shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________          Immediately                                                             Liquid                                                                              after                                                                   Sucking-up                                                                          Storage of                                                                           1 day                                                            Member                                                                              City Water                                                                           (Number)                                                                            3 days                                                                             7 days                                                                              20 days                                         __________________________________________________________________________    free of                                                                             0      4 × 10.sup.3                                                                  5 × 10.sup.4                                                                 more than                                                                           more than                                       bacteri-                5 × 10.sup.4                                                                  5 × 10.sup.4                              cide                                                                          No. 1 0       0     0   0     0                                               No. 2 0      35    10   0     0                                               No. 3 0       0     0   0     0                                               No. 4 0      70    35   6     1                                               No. 5 0      40    25   2     0                                               __________________________________________________________________________

As is clearly seen from Table 1, when the liquid sucking-up member isimparted with a bactericidal property as in the present invention,bacteria are prevented from propagating. Wnen the steam generator isapplied as a humidifier, almost no bacteria are released in room, thusbeing very good for health.

EXAMPLE 3

The corrosion resistivity of the heating unit 13 was tested. As testsamples, there were provided the heating unit of Example 1 (No. 1 ofTable 2 shown below), the heating unit 13 of Example 1 which weresubsequently covered with a sealant 23 made mainly of ethylenetetrafluoride resin in a thickness of 20 μm (No. 2 of Table 2), and acoil-like winding of Ni-Cr wire (No. 3 of Table 2).

Those three units were tested.

The experiment was conducted by a salt spray test using a 3% NaClsolution in an atmosphere of 80 C and an increasing amount of oxide 10days after the test was measured. The results are as shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                 Sample                                                                        No. 1      No. 2   No. 3                                             ______________________________________                                        amount of  0.05         0.00001 0.1                                           oxide                                                                         (mg/cm.sup.2)                                                                 ______________________________________                                    

As will be apparent from the above test results, the heating unit usedin the present invention is highly resistant to corrosion. Especially,the heating unit which was filled with the sealant 23 mainly composed ofethylene tetrafluoride resin was very excellent in corrosionresistivity.

<EXAMPLE 4>

In case where the heat generator of the present invention is applied asan inhaler for the respiratory organs, the fan of FIG. 1 is stopped andthe power consumption for the heating unit 13 is controlled at 100-150W, whereupon steam is vigorously jetted out from the discharge port 3.The discharge port 3 is made narrow at the tip thereof so that steam canbe jetted out, and in front of the discharge port 3 is provided a thintube through which a medical solution such as a saline solution or anaqueous adrenaline solution is sucked up.

INDUSTRIAL APPLICATION

As having been described hereinabove, according to the invention, therecan be provided a steam generating apparatus which can generate steamefficiently in a short time and is applicable as humidifiers orinhalers.

We claim:
 1. A steam generator comprising a container having an uppervaporization chamber and a lower liquid storage chamber, means forpartitioning the upper and lower chambers from each other, saidvaporization chamber having a gas charge inlet port enabling a gas to becharged into said vaporization chamber and a discharge port fordischarging steam generated within said vaporization chamber; a suck-upmember disposed to extend into the upper and lower chambers within saidcontainer so that one end portion of said suck-up member is immersed ina liquid contained in said lower storage chamber while the other endportion extends into the upper chamber; and heating unit means providedat said other end portion of the suck-up member for heating andvaporizing the liquid absorbed by the suck-up member at the one endportion when it reaches the other end portion of said suck-up member,said heating unit means being in the form of a wire or band and a metaloxide or metallic double oxide layer formed on said wire or band tothereby increase the surface area of the heating unit means in contactwith the liquid and improve thermal transmission to vaporize the liquid,said vaporized liquid being entrained by a gas passed through said gascharge port for discharge through said discharge port.
 2. A steamgenerator according to claim 1 further including gas supply means forcharging gas into the vaporization chamber to provide a gas flow rategreater than approximately 0.1 m/sec at a point where the gas contactsthe suck-up member.
 3. A steam generator according to claim 1, whereinsaid suck-up member is made of an inorganic material having capillaryaction and selected from the group consisting of glass fibers,alkali-proof fibers, silica fibers and alumina fibers.
 4. A steamgenerator according to claim 3, wherein said inorganic material is inthe form of cloths or fabrics.
 5. A steam generator according to claim1, wherein said suck-up member is made of at least one member selectedfrom cloths or fabrics of materials selected from the group consistingof novolac fibers, metallic fibers, ceramic fibers, asbestos and carbonfibers, heat-resistant porous materials and foamed materials.
 6. A steamgenerator according to claim 1, 3, 4 or 5 wherein said suck-up member isconstituted of a material having a water suction rate greater thanapproximately 1.0 mm/sec.
 7. A steam generator according to claim 1,wherein said wire or band is made from material selected from the groupconsisting of Ni-Cr, Fe-Cr, Fe-Cr-Al, Fe-Cr-Al-Y and stainless steel. 8.A steam generator according to claim 7, wherein said metal oxide ormetallic double oxide is in the form of a spray-coating on said heatingmember.
 9. A steam generator according to claim 7, further comprising aheat-resistant alloy layer provided between said heating member and saidmetal oxide or metallic double oxide layer.
 10. A steam generatoraccording to claim 7, wherein a sealant layer is formed on said metaloxide or metallic double oxide.
 11. A steam generator according to claim10, wherein said sealant layer is made of a fluorine-containing resin.12. A steam generator according to claim 11, wherein saidfluorine-containing resin includes at least one member selected from thegroup consisting of ethylene tetrafluoride resin, propylenetetrafluoride copolymer resin and ethylene trifluoride resin.
 13. Asteam generator according to claim 1, wherein said heating unit means issubstantially covered by a portion of said suck-up member extendingaround the outer surface thereof.
 14. The apparatus of claim 1, whereinsaid such up member includes a wick having capillary action to draw andcontain liquid within the vaporization chamber.
 15. The apparatus ofclaim 14, wherein said heating means is disposed within ambient air inthe vaporization chamber.
 16. The apparatus of claim 1, wherein saidupper and lower chambers are substantially entirely partitioned fromeach other so that the only liquid communicating directly with thevaporization chamber is substantially contained within the suck-upmember.